Currently, some diagnostic and therapeutic catheters are manufactured by forming braided tubes of stainless steel fibers or strands over a mandrel. More specifically, the braided tube may be formed about an inner Teflon.RTM. liner or tube initially carried on a supporting mandrel. An outer plastic layer may then be extruded about the braided layer to create the catheter body. Current catheter constructions also utilize a transition tip which is not reinforced with braid in order that the tip be softer and more flexible than the remaining portions of the catheter. In some catheter designs, an even softer more flexible tip is bonded to the free end of a relatively soft tubular "transition" tip.
Catheters which incorporate multiple axial sections of the outer layer typically employ butt or lap weld joints to secure such sections together. See, for example, U.S. Pat. Nos. 5,254,107; 4,861,337; 4,793,351; 4,662,404; and 4,391,302. Catheters incorporating either butt or lap type welded joints are not completely satisfactory however. In commonly owned U.S. Pat. No. 5,772,641 (incorporated herein by reference), improved catheter constructions are disclosed which incorporate unique weld configurations which have substantial axial seam components which extend along the axis of the catheter (either parallel to the catheter axis or at an acute angle to the axis). In other words, adjacent outer catheter sections are cut and welded in such a way that they overlap in the longitudinal direction, but without altering the outer diameter of the catheter. This arrangement not only increases surface area at the weld joints to increase bond integrity, but also creates a more desirable transition between axial sections formed of the same materials of different durometer, or different materials with or without the same durometer. The unique joint seam configurations also permit alteration of properties or characteristics of the material in the areas of the joints themselves (thus creating an "intermediate section" or transition area between axially adjacent sections), and this feature is particularly advantageous in areas of the catheter that will be curved or bent in use, in that different stiffness or hardness materials can be used on the inside and outside of the curve. In the '641 patent, however, the unique weld configurations are specified only for the layer of the catheter lying radially outwardly of the braid layer.
In accordance with this invention, further improvements in joint configurations (referred to herein as "scarf joints") are accomplished in a manner which maximizes weld strength while creating even more favorable transitions between tubular sections. In particular, we have now discovered that it is possible to join a braid layer (for example, a stainless steel braided tube), to a non-braided section or to a catheter "tip," utilizing tapered or scarf joints of the type generally disclosed in the '641 patent. More specifically, the tapered or scarf cut can be effected not only in the radially outer plastic layer, but also within the inner braid layer as well. Using heat shrink Teflon.RTM., as is common in tip welding (or other suitable techniques including adhesives with or without the application of heat; passing the assembly through a heated die, etc.), the scarf cut braid layer may be joined or bonded to the axial non-braided tube (or even to another braided tube). In this regard, the stainless wire braid is annealed so that loose ends at the taper or scarf cut do not spring radially outwardly into and/or through the outer plastic layer. Other techniques for keeping the loose ends in place could be employed as well. In addition, however, higher tensile strength wire could be utilized with heat insensitive adhesives.
By employing the scarf cut through the inner braid layer, additional benefits are achieved in terms of varying the flexibility of the catheter along its length, and particularly in transition areas between axial sections.
In an exemplary embodiment of the invention, a relatively stiff braided section is scarf-welded to a moderately stiff non-braided section which, in turn, is scarf welded to a "soft" section or simply tipped with a butt welded soft tip. The number of braided and non-braided sections may vary, however, as dictated by specific applications.
Accordingly, in its broader aspects, the present invention relates to a catheter having at least two lengths of tubular material axially joined together by a scarf joint with no perceptible change in outer diameter at the joint, the scarf joint including a substantially axially oriented seam component between the two lengths of tubular material with the seam visible along the peripheral surfaces of the axially joined sections and extending at an acute angle to the longitudinal axis of the catheter; and wherein one of the at least two lengths of tubular material includes an inner tubular reinforcement layer, wherein the reinforcement layer forms part of the scarf joint.
In another aspect, the invention relates to a catheter having at least two adjacent lengths of tubular material axially overlapped and joined together by a scarf joint, the lengths of tubular material having continuous outer surfaces and a lumen extending along a longitudinal axis, the scarf joint including a seam on the outer surfaces extending more than 0.5 cm in length and at an acute angle to the longitudinal axis of the catheter such that each of the at least two adjacent lengths form substantially half of the catheter along the scarf joint, and wherein the two lengths of material are of different composition with different mechanical properties, thereby establishing an intermediate section having variable properties along the scarf joint; and wherein one of the at least two adjacent lengths of tubular material includes an inner reinforcement layer.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.